Preparation of a bistable ferrite circuit element



July 3, 1962 J. M. BROWNLOW 3,042,513

PREPARATION OF A BISTABLE FERRITE CIRCUIT ELEMENT Filed June 9, 1959 2 Sheets-Sheet 1 FERRITE POWDERS WETBALL MILL I E I J I I DRY I I T I CALCINgAT @1 UL L J T SPINEL I I mx WITH RESINOUS I BINDER AND SOLVENT I l CUT mm I DESIRED SHAPE E I I l I FIRE AT I I I000-I500C I HIGH SPEED FERRITE STORAGE ELEMENT July 3, 1962 J. M. BROWNLOW 3,042,518

PREPARATION OF A BISTABLE FERRITE CIRCUIT ELEMENT Filed June 9, 1959 2 SheetsSheet 2 AP AP FIG. 1 FIG.1O FlG.1b

FlG.1c FlG.1d PIC-lie FIG. if

B AB

H applied 5 FIG. 2b

ATTORNEY atent Ofifice 3,042,618 Patented July 3, 1962 3,042,618 PREPARATIQN A BESTABLE FERRITE CIRCUIT ELEMENT James M. Browniow, Fishkiil, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed .iune 9, 1959, Ser. No. 819,056

3 Claims. (Cl. 252-525) This invention relates to high speed, bistable circuit elements and more particularly to a small, high speed ferrite computer storage and switching element.

Since the discovery that certain ferrite materials in the form of toroidally-shaped cores exhibited the characteristics required for operation as a memory material in computer circuitry, in particular, the rectangular hysteresis loop, it has been the object of considerable research to provide new and improved ferrite memory elements.

Particularly sought after are memory elements exhibiting high switching speeds. With such high-speed elements it is possible to design computers consisting of a few simple circuits which may be used over again to perform desired operations. For example, if high-speed elements were available, a serial adder could be used instead of the more complicated parallel adders now being used.

While it is known that certain thin metallic films inherently possess these high-speed characteristics, their use in application appear at present to be limited by certain operational difficulties, such as the problem of disturbed sensitivity or partial switching during half selection in the coincident-current selection scheme. It is desired, therefore, to provide memory elements for computer circuitry Which combine the advantages of the presentlyused ferrite elements and the high-speed thin metallic films.

What is described hereinafter is a'high-speed switching element composed of ferrite material. The element may take the form of open flux path rods, bars, fibers which have rcmanence in the plane of the element or in the form of thin toroids with closed flux paths. These elements exhibit these characteristics within certain dimensions, particularly when the thickness of the element is below 25 microns.

The open flux path elements are particularly amenable to printed circuit wiring techniques, which is of a distinct advantage in fabrication of large-scale memory arrays for computer circuits. In addition to their unusually high speed operation, the elements of the present invention produce sharp output voltage characteristics and negligible disturbed sensitivity during half select operations, characteristics which make these elements more desirable for large-scale memory arrays than presently available memory elements.

Another characteristic of the computer circuit element of the present invention is that its hysteresis loop possesses a very high degree of squareness.

A method is described herein for preparing these elements, said method comprising mixing the ferrite powders in a predetermined ratio, calcining the mixture in air at elevated temperatures to form the spinel structure, mixing a suitable resinous binder and solvent therewith, applying the mixture to a support surface, drying, cutting into desired sizes and shapes, separating the parts from the support surface and firing the parts in a suitable boat at elevated temperatures.

Accordingly, an object of the present invention is to provide a high-speed storage and switching element.

Another object of the present invention is to provide a high-speed, open flux path ferrite memory element having very high remanence in the plane of the element.

A further object is to provide an open flux path ferrite memory element having a switching constant, S in the order of 0.15 oersted-microsecond, said element having remanence in the plane of the element and a thickness of less than 25 microns.

Still another object of the present invention is to provide a high-speed, closed flux path ferrite memory element, such as a toroid.

Yet another object is to provide a closed flux path ferrite memory element having a switching constant, S in the order of 0.15 oersted-microsecond, said element having a thickness of less than 25 microns.

Among the other objects of the present invention is to provide an open flux path ferrite memory element having high speed switching characteristics, and which may be selectedby conventional coincident-current techniques.

A more specific object is to provide a high speed switching, low coercive force, rectangular hysteresis loop, square knee, memory element, said element taking the geometrical shape of a bar having a thickness of less than 25 microns and a length-to-width ratio of greater than 5.

Still another object of the present invention is to provide methods for preparing these ferrite elements.

Another specific object of the present invention is to provide a method by which an open flux path, square hysteresis loop ferrite memory elements may be prepared, which method comprises mixing the ferrite powder in predetermined ratios, calcining the mixture in air at elevated temperatures to form the spinel structure, mixing a resinous binder and a suitable solvent therewith applying the mixture to a support surface, drying, cutting into desired shapes and firing at elevated temperatures.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1(a-f) shows the various geometrical forms that the high-speed switching element of the present invention may assume.

FIGURE 2 is a reproduction of an actual 60-cyc1e hysteresis loop obtained from these elements; the particular loop shown being obtained on body number 103 having a thickness of 25 microns given in Table I.

FIGURE 2a shows a similar loop for a body of 50 microns thickness, namely T14A shown in Table III.

'FIGUR-E 2b is a switching plot of l/T vs. H appged for body 103 of Table I (curve A), for thin toroids (B) and thick toroids (C).

FIGURE 3 is a flow chart illustrating the process by which the elements of the present invention may be 7 prepared.

Referring now to FIGURES l(af) there is shown in graphic representation some of the geometrical forms that the highspeed circuit element of the present. invention may assume. These elements are prepared within certain specified predetermined dimensions which will be described hereinafter. Within these dimensions the elements exhibit switching constants in the order of 5 times smaller than conventional thick toroidally shaped ferrite cores presently used as memory materials in computers. In addition the elements of the present invention exhibit a higher degree of hysteresis loop rectangularity, which permits use of coincident-current selection raitos less than the presently used 2:1 ratio. As for example 4:3 may be used in coincident-current memory arrays with the present elements.

Another characteristic .of the element of the present invention is that they may be made in a form which exhibits an open flux path, the remanent state of which lies substantially in the plane of the element. This magnetic behaviour results in improved pulse performance, in particular, a sharp spiked output signal. Furthermore aoeaeis 3 smaller disturbed sensitivity is observed with half select pulses. The degree of non-shearing of the hysteresis loop may be optimized by proper adjustment of the geometrical dimensions of the element.

4 ing of the parts of the platinum, and sintered at elevated temperatures, in the range 'of 1000 to 1500 C., for 5 minutes to three hours, and thereafter cooled to room temperature to form the final product.

The elements described herein may be prepared by the 5 With reference to the generalized flow sheet shown in following process: FIGURE 3 the following specific example will illustrate Suitable metallic oxides, as for example, magnesium the process: oxide, manganese sesquioxide and ferric oxide are mixed Magnesium oxide, 32.2 grams, manganese sesquioxide, in suitable predetermined proportions in accordance with 38.7 grams, and ferric oxide, 135.7 grams, corresponding the ratios used in the conventional ferrite systems presentto the formula Mg 3MH 5F1 qQ4, were intimately mixed. ly used as thick toroids. The'rnixed oxides are ball milled The mixture was Wet ball milled for ten hours, oven in water, dried and calcined in air at 800-1400" C. to dried at 110 C. for 2 hours and calcined in air at 1000 form the desired spinel compound. The mass is then re- C. for three hours. The mass was repulverized to a pulverized with a resinous binder and solvent. The binder fine powder and mixed with 40 grams of pyroxylin and comprises between 5 and 50% by weight of the spinel 500 grams of amyl acetate. The thin slurry was ball powders and the solvent between /2 and 4 times by weight milled for four hours, then poured onto a glass surface of all dry materials, including resin and ferrite. The per covered with a thin layer of gelatin, placed on a spinning centage of the binder and solvent 'is chosen such that table and spun dried. The resulting thin sheet of ferrite the ferrite particles touch each other but do not agglomwas then cut into bars having a length of 0.75 inch, a crate. Suitable binders and solvents, respectively, in- 2 width of 0.12 and a thickness of 0.0004 inch. The bar clude nitrocellulose resins such as pyroxylin, and amyl ferrite elements were then separated from the support acetate, alkyd resins and toluene and polyvinyl alcohol surface by dissolving out the gelatin with warm water. and water. The ferrite-binder-resin mixture is reball The individual parts were then placed in a platinum boat milled for 2 to 10 hours to further subdivide the mixture lined wtih alumina, sintered at 1400 C. for five minutes and poured or sprayed onto a glass or other suitable supand slowly cooled to room temperature. port medium on a spinning table and spun until dry. Using the general method described above a number The resulting sheet or film is then cut into the desired of ferirte elements of varying compositions, sizes and size and shape, as for example, into thin fibers, rods, bars, shapes, as shown in Table I, were prepared. tol'oids- The Parts are thereafter Separated fr m h Table 11 shows some pulse test data obtained for open support surface prior to final sintering. A convenient fl h f it ekmems of the composition way to accomplish this separation is to pretreat the glass surface with a 1-4% gelatin-water solution prior to appli- M gMn F O, cation of the ferrite dispersion. The parts are then transferred to a firing container, such as an alumina lined Table III presented below shows the efiect of varying platinum boat, the alumina being used to prevent stickthe thickness of bar ferrite elements on loop squareness.

TABLE I Physical Properties of the High Speed Ferrite Element of the Present Invention B d Firing Conditions H B B Switching o y a i i Constant Length Width L/W Thick- Number Formula in Atom Numbers (Oer) (gauss) (gauss) B,/B SW, (0er.) L (in.) W (in.) Ratio ness, T

Temp. Time (uSeCJ (microns O.) (Mm.)

Mg Mn Fe O 1, 400 5 3. 0 3, 000 2, 700 90 0. 12 0. 75 012 9. 0 Mg.sMn,5Fei.1O4 1, 400 5 3. 0 3, 000 2, 400 8 0. 15 0. 025 30 9. 0 Mg.sMn Fe1.10i 1, 400 5 3. 0 3,000 2, 200 73 0. 15 0. 75 060 10 9. 0 Mg.sMn, Fe1.7 4.. 1, 400 60 2. 0 3, 000 2, 500 83 0. 15 0. 390 015 26. 0 9. 0 MEJMHJFQ! 70 1, 400 15 3. 2 3, 000 2, 700 90 0.15 0. 5 025 20. 0 9. 0 Mg slvlusFe 70 1, 400 15 3. 3 3, 000 2, 700 90 0. 15 0. 400 030 13. 3 4. 0 Mg g AIILEFGI 704.- 1, 400 15 3. 3 3, 000 2, 400 0. 15 0. 625 0250 25. 0 4. 0 Mg sMImFe; 1Oi 1, 400 60 2. 6 3, 000 2, 700 0. 15 0. 500 020 25. 0 9.0 Mg iMn Fe 104.- 1, 350 1200 1. 6 3, 000 2, 700 90 0. 15 0. 55 020 27. 5 9. 0 Mgi1 Mn1.oZnu .3O4 1, 400 10 2. 0 2, 000 1, 600 0. 80 O. 20 0. 50 020 25. 0 9. 0 Mm.2nClo.oo5N1e.0fi5Fei.na 4- 1, 400 20 3. 0 2, 500 1, 750 0. 75 0. 18 0. 50 020 25. 0 9. 0 'Ou M11i.2aFei .7004 1, :08 231 3. 0 2, 500 1, 750 O. 75 0. l2 0. 50 010 50. 0 9. 0 Mg9 Ni,23Ti,zFe u204 1 38 6 6.0 2, 000 1,400 0. 75 0. 50 .020 25. 0 9. 0

TABLE II Pulse Data Thickq q Body No. Length Width L/W ness T, mg Tune mg Tune Ho Discrim.

L (111.) (111.) (microns) 3-1 2-1 (0st.) Ratio (msec.) (msec) Il -Threshold field=maidmu n field for which no irreversible switching occurs.

Ts, Switching time for applied field of 3H0. Measured as the duration of the output voltage pulse between 10- amplitude points when the element is driven by square ulses.

T.-,, ,-Switching time for applide field of 2110. Measured in the same way. p Discrimination Ratio is defined as the ratio or voltage output obtained when the element is readout from the undisturbed 1 remanence state to the voltage output obtained when a positive half select pulse is applied to the element in the disturbed 0 remauence state TABLE III Efiect of Varying the Thickness of Bar Ferrite Elements on Loop Squareness 16 No shearing (Similar to Fig. 2).

As shown in the tables the ferrite element of the present invention exhibits exceedingly fast switching characteristics as well as a high degree of loop squareness. The data in Table II in particular indicates the suitability of the element for operation in coincident-current memory arrays. For this application as shown by the fi /B ratio of bodies 103, 103A and 103B of varying L/ W ratios presented in Table I, it is desirable that the L/ W ratio be greater than 5 and the thickness be kept below microns. Table HI shows the effect of increasing the. thickness of the element. At a thickness of 50 microns the hysteresis loop is sheared considerably. For application other than memory it may be possible to tolerate this shearing effect and thereby take advantage of the exceedingly fast switching characteristics of the element.

FIGURE 2 illustrates the switching characteristics of the element of the present invention, in particular, curve A is presented to show the switching characteristics of body 103. Curve B shows the effect of reducing the thickness of toroids, in particular a toroid of composition represented by body 103 and having a thickness of 18 microns. Curve C shows the switching characteristics of thick toroids (500 microns) of the same 103 compositions. The switching speeds of the latter are of the order of 5 times slower than the elements of the present invention.

Another characteristic of the open flux path ferrite element whose geometrical shapes are illustrated in FIG- URE 1ae is that they exhibit a uniaxial shape anisotropy in the plane of the element with this property these elements may be utilized in place of thin metallic films in thin film memory arrays. Such'circuits are better than the circuits using metal films in that the output voltage responses are much sharper and the disturbed sensitivity reduced as compared to thin metal film circuits.

What has been described herein is a unique, high-speed, ferrite memory element particularly suited for operation as a memory component in computer circuitry. While we have described our invention with particular reference to open flux path elements, thin toroidally shaped ferrites have also been shown to exhibit the same properties.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of preparing a high speed, ferrite memory element having a thickness less than 25 microns which comprises mixing selected metallic oxides in predetermined ratios, calcining the mixture in air at elevated temperatures to form the spinel structure, mixing a resinous binder and a suitable solvent therewith, said oxides touching each other but not agglomerate in said. binder and solvent applying the mixture to a support surface to form thereby said element within said thickness drying, cutting into desired shapes, removing said support, and firing at elevated temperatures.

2. A method of preparing a high speed, open flux path, substantially rectangular hysteresis loop, ferrite memory element having a thickness less than 25 microns which comprises mixing selected metallic oxides in predetermined ratios, calcining the mixture in air at 8001400 C. to form the spinel structure, repulverizing the mass with a resinous binder comprising between 5 and by weight of the spinel powder and a solvent for said binder comprising between /2 to 4 times the weight of all dry materials, including said binder and said spinel powders, remixing the mass for 2 to 10 hours, applying the mixture to a support surface to form thereby said element within said thickness drying, cutting the resultant film into desired shapes, separating the shapes from the support surface, transferring the shapes to an aluminalined platinum boat and sintering the parts at 1000 1500 C. for 5 minutes to 3 hours.

3. A method of forming a high speed, open flux path ferrite memory element which comprises the steps of mixing 32.2 grams of magnesium oxide, 38.7 grams of manganese sesquioxide and 135.7 grams of ferric oxide, corresponding to formula Mg Mn Fe O wet ball milling the mixture for 10 hours, oven drying at for two hours, calcining in air at 1000 for three hours, repulverizing the mass to a fine powder, mixing. 40 grams of pyroxylin .and 500 grams of amyl acetate therewith, ball milling for four hours, pouring onto a glass surface covered with a thin layer of gelatin, placing on a spining table, spin drying, cutting the resultant thin sheet of ferrite into bars having a length of 0.75 inch, a width of 0.12 inch and a thickness of 0.0004 inch (9 microns), separating the bar ferrite elements from the support surface by dissolving out the gelatin with warm water, placing the individual elements in a platinum boat lined with alumina, sintering at 1400" C. for five minutes and slowly cooling to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,770,523 Toole Nov. 13, 1956 2,842,500 Gibson et al July 8, 1958 2,961,709 Eichbaum et al Nov. 29, 1960 2,978,414 Harz et a1. Apr. 4, 1961 FOREIGN PATENTS 556,756 Canada Apr. 29, 1958 697,219 Great Britain Sept. 16, 1953 737,284 Great Britain Sept. 21, 1955 788,727 Great Britain Jan. 8, 1958 789,099 Great Britain Jan. 15, 1958 

3. A METHOD OF FORMING A HIGH SPEED OPEN FLUX PATH FERRITE MEMORY ELEMENT WHICH COMPRISES THE STEPS OF MIXING 32.2 GRAMS OF MAGNESIUM OXIDE, 38.7 GRAMS OF MANGANESE SESQUIOXIDE AND 135.7 GRAMS OF FERRIC OXIDE, CORRESPONDING TO FORMULA MG8MNFE1.7O4, WET BALL MILLING THE MIXTURE FOR 10 HOURS, OVEN DRYING AT 110* FOR TWO HOURS, CALCINING IN AIR AT 1000* FOR THREE HOURS REPULVERIZING THE MASS TO A FINE POWDER MIXING 40 GRAMS OF PYROXYLIN AND 500 GRAMS OF AMYL ACETATE THEREWITH, BALL MILLING FOR FOUR HOURS POURING ONTO THE GLASS SURFACE COVERED WITH A THIN LAYER OF GELATIN, PLACING ON A SPINING TABLE, SPIN DRYING CUTTING THE RESULTANT THIN SHEET OF FERRITE INTO BARS HAVING A LENGHT OF 0.75 INCH A WIDTH OF 0.12 INCH AND A THICKNESS OF 0.0004 INCH (9 MICRONS), SEPARATING THE BAR FERRITE ELEMENTS FROM THE SUPPORT SURFACE BY DISSOLVING OUT THE GELATIN WITH WARM WATER, PLACING THE INDIVIDUAL ELEMENTS IN A PLANTIUM BOAT LINED WITH ALUMINA, SINTERING AT 1400*C. FOR FIVE MINUTES AND SLOWLY COOLING TO ROOM TEMPERATURE. 